It is common to group modern telecommunication equipment together in the same chassis, housing, or building. For example, in base stations of cellular telecommunications systems, there may be a small building that houses a variety of types of telecommunication equipment grouped together in one or more telecommunication rack or chassis. A central office (CO) may include a much larger building with multiple racks of telecommunication equipment and telecommunication chassis, each rack containing multiple telecommunication circuit cards that may perform different functions. In each of these and other situations, the telecommunication equipment within a single building may all be powered by the same power source, such as an AC/DC power converter or DC batteries.
In such situations, equipment in one telecom chassis may add electrical noise to the DC power lines, which may be passed to other telecom chassis that are connected to the same DC power source. Telecom organizations have set standards for the acceptable level of electrical noise that can be passed by a telecommunication device.
Traditionally, telecom circuit cards have been designed to have power filtering thereon. More recently, it has become desirable to have power filtering instead performed at the chassis level, in order to allow more flexibility in design for the telecom circuit cards. Typically, Y2 isolation capacitors have been used in power filters, in part because of their ability to handle high voltages and because, when they fail, they fail in a predictable fashion that results in an open circuit. Unfortunately, however, Y2 isolation capacitors are very large in volume relative to other types of capacitor and they provide a low amount of capacitance relative to similarly sized capacitors of other types.
When building a power filter at the chassis level, the volume required to do all of the filtering with Y2 isolation capacitors would be impractical. Conversely, if the power filtering were not performed with capacitors, then very large inductors would be needed. Unfortunately, this would also be impractical, due to the large volume and expense of the inductors. Furthermore, conventional power filters have included field effect transistors (FETs) in series with the load in order to reduce the in-rush current into the filter capacitors. But with the large amount of current flow through and filtering required of power filters at the chassis level, the power dissipation and heat generated by such FETs in series with the load can become unacceptable for a large chassis.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.